Floor joists are an important part of the supportive structure of a floor. They hold up the weight of a building, absorb impacts on the floor, and create structural support so that the floor will be stable and secure. Joists are installed at a very early stage in the building process, and in older structures, they may eventually need to be replaced as a result of wear, or if they were installed improperly when the building was constructed. Many people never see them, unless they are involved in remodeling and construction projects.
These structural elements of a building make up part of the subfloor, the structure that goes underneath the flooring that people walk on. Subfloors are designed to provide support to the flooring, and to make the building itself more rigid and stable so that it will withstand years of heavy use. Joists are typically run perpendicular to beams, and they connect with the supportive framework of the structure to reinforce it.
It is very important to install floor joists properly. Their spacing is critical to engineering safety, and they must be perfectly flat and level, or the floor will be uneven. High quality wood must also be used, as bending and warping in the joists will throw the floor and the building out of plumb, causing structural problems and safety issues. In addition, contractors have to think about ease of access for repairs and other projects when they install the subfloor.
Plumbing, electrical lines, and ductwork may be installed in the subfloor at the time it is built, or on a later date. Thinking about these issues ahead of time is important when the building is erected, as badly-placed joists can make construction much more difficult than it needs to be. Contractors also have to think about issues such as the potential for water intrusion into the subfloor, which can cause structural problems with the building.
A number of different products can be used for floor joists. Wood is a classic material of choice, and it continues to be widely used around the world. It is also possible to use various fabricated metal products, along with specially engineered plastics. In all cases, reputable contractors will use materials that satisfy or exceed the building code, and they will take care when installing the joists and the other elements of the subfloor to reduce the need for maintenance in the future.